Multi-scale phenotype-substrate matching: evidence from shore crabs (Carcinus maenas L.)

Phenotype-environment correlations can be caused by various overlapping ecological processes (e.g. differential mortality, phenotypic plasticity and adaptation) operating over a range of spatial and temporal scales. However, multi-scale studies of the relationship between specific traits and environmental variables are rare, even though such a holistic view may have greater predictive value than the more typical single-scale observations. Here, we investigate the relationship between cryptic colouration and environmental characteristics at a range of spatial scales for the shore crab (Carcinus maenas L.), a common intertidal species. Using existing data sets at macro-scale (10,000sm²) and meso-scale (100sm²) and previously unpublished data at a micro-scale (<1m²) we demonstrate that phenotype-substrate associations in this species are sampling-scale invariant. The association is strongest at the micro-scale, possibly because the advantages of cryptic colouration for visual predator avoidance are dependent on close concordance between prey phenotype and the surrounding substrate. By contrast, correlations at greater spatial scales may reflect longer term processes such as phenotypic plasticity or the accumulated effects of predator mediated differential mortality.